[MemorySSA] Add APIs to move memory accesses between blocks, following CFG changes.

Summary:
The move APIs added in this patch will be used to update MemorySSA when CFG changes merge or split blocks, by moving memory accesses accordingly in MemorySSA's internal data structures.
[Split from D45299 for easier review]

Reviewers: george.burgess.iv

Subscribers: sanjoy, jlebar, Prazek, llvm-commits

Differential Revision: https://reviews.llvm.org/D48897

llvm-svn: 336860

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/MemorySSA.cpp b/llvm/lib/Analysis/MemorySSA.cpp
index fe89c1d9570..f57d490ce96 100644
--- a/llvm/lib/Analysis/MemorySSA.cpp
+++ b/llvm/lib/Analysis/MemorySSA.cpp
@@ -1473,8 +1473,18 @@ void MemorySSA::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
   insertIntoListsBefore(What, BB, Where);
 }
 
-void MemorySSA::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
+void MemorySSA::moveTo(MemoryAccess *What, BasicBlock *BB,
                        InsertionPlace Point) {
+  if (isa<MemoryPhi>(What)) {
+    assert(Point == Beginning &&
+           "Can only move a Phi at the beginning of the block");
+    // Update lookup table entry
+    ValueToMemoryAccess.erase(What->getBlock());
+    bool Inserted = ValueToMemoryAccess.insert({BB, What}).second;
+    (void)Inserted;
+    assert(Inserted && "Cannot move a Phi to a block that already has one");
+  }
+
   removeFromLists(What, false);
   What->setBlock(BB);
   insertIntoListsForBlock(What, BB, Point);